1. Field of the Invention
This present disclosure relates to an insulation state detecting device using a flying capacitor.
2. Description of the Related Art
For example, a vehicle that uses electrical power as energy for driving such as an electric car may be provided with a DC power supply device which outputs a high voltage of around 200V. The vehicle provided with the DC power supply device of such a high voltage is used when the positive and negative power lines of the DC power supply device are electrically insulated from the vehicle body. That is, the vehicle body is not used as the ground of the power source for outputting high voltage power.
In such a vehicle, to ensure safety, it is necessary to check to ensure that the wires for the DC power supply output of the high voltage are sufficiently insulated from the vehicle body. Related techniques of insulation state detecting devices for checking in the above situation are known as JP-B-3962990 and JP-A-2011-21990.
This kind of insulation state detecting devices use a flying capacitor. That is, through a switching element, a detecting capacitor (referred to as the flying capacitor) is connected between the positive and negative power lines for the high voltage and a ground electrode (the vehicle body) only for a predetermined time. The charge voltage of the flying capacitor is monitored, and ground fault resistances, namely, the insulation resistances between the power lines and the ground electrode are calculated from the charge voltage.
To remove the high frequency noise of the power supply, and to stabilize operations of the power supply, capacitors called Y capacitors (line bypass capacitors) are often connected between the positive and negative power lines for the high voltage and the ground electrode (in JP-A-2011-21990).